It is known, in the prior art, to use a progressing cavity type pump in which a rotor rotates within a stator to discharge material from a hopper or other supply source. Prior to this invention, however, the art had found no way to discharge material using such a pump without having one or more of the flexible joints connecting the rotor to an appropriate drive means immersed in the material being discharged.
A typical progressing cavity pump is shown in U.S. Pat. No. 1,892,217 to Moineau; another pump of this type is shown in U.S. Pat. No. 2,483,370, also to Moineau.
Basically these pumps include a stator having an inner double helically threaded surface and a helical rotor having a constant diameter circular cross section positioned within the stator. The rotor is adapted to rotate eccentrically within the stator, when driven by an appropriate drive means, through a flexible joint, and as the rotor rotates and orbits, it generates progressing cavities which deliver the material to the discharge point.
Means to accommodate the eccentric orbiting or wobbling of the rotor must be provided. Many solutions are known to the art. The commonest is a set of universal joints of the Cardan type to provide two spaced pivotal connections, as disclosed in U.S. Pat. No. 2,028,407 to Moineau. These universal joints allow the rotor to orbit; the stator is fixed. Other types of universal joints may be used, such as the cross-slide shown in U.S. Pat. No. 3,567,348 to Benson. Another solution is a flexible one-piece shaft also as shown in U.S. Pat. No. 2,028,407 to Moineau, U.S. Pat. No. 3,600,113 to Pahl, or U.S. Pat. No. 3,612,734 to Dawson et al., for example. It further has been proposed to rotate the outer member of the pump as in U.S. Pat. No. 3,932,072 to Clark. The inner member then is constrained to wobble; one end is free, and the other is prevented from rotating but may pivot about a point which is permitted to reciprocate.
Two types of stators are known to the art. Moderate to high pressure pumps may employ tube or rigid stators. The double helical surface in such instances is formed in a rigid material or in a resilient or elastomeric material encased in a rigid tube. Low to moderate pressure pumps have the stator fully molded in a resilient material. These frequently are called wobble stators and are further described in a "Ramoy Pumps" catalog, dated April 1979.
Two forms of these latter pumps exist. In one, the rotor has no wobbling motion; the stator wobbles or gyrates, sweeping out a cylindrical orbit. In the other, as shown at pages 6, 8, 9, 10, 11 and 12 of the "Ramoy Pumps" catalog, for example, the rotor is connected to the drive means through a flexible joint positioned in the flow path of the material being discharged and wobbles in a conical orbit with its apex at that joint. The stator, on the other hand, is constrained in a manner whereby it orbits in a conical orbit which has its apex on the centerline of the stator extended to an imaginary point. The cone swept out by the stator is inverted relative to the cone swept out by the rotor.
In many industrial situations, it is particularly convenient to discharge a hopper from the bottom and where the material is viscous or must be metered, it is common to mount a pump on the bottom discharge outlet of such hopper. Often it is necessary to drive such a pump from above with the drive train including the required universal joint extending through and in the pumpable fluid.
Such as arrangement is shown in U.S. Pat. No. Re. 24,079 to Mateer. One or both of the requisite universal joints, which provide the rotatable pivotal connections needed to accommodate the eccentric or orbiting motion of the rotor is submerged in the pumpable fluid. These joints are shielded from the fluid by means of boots of fluid-resistant flexible material in those instances where it is necessary to prevent the fluid from getting inside the joint. This shielding is mandatory when an explosive material such as water gel or other liquid explosive is pumped.
Further, when pumping a liquid explosive, it is imperative to avoid shaft seals in the pump wetted by the liquid. It is equally important to avoid dead spaces within the pump. Thus the pumps previously describe in the "Ramoy Pumps" catalog are not adaptable to this use and a drive design such as the one shown in Mateer is used. The submerged boot protecting the universal joint, however, may fail in service and since it cannot be seen by the operator, such an occurrence would permit explosive to enter the joint itself with the possibility of an explosion.
This invention solves these problems by positioning the flexible joint connecting the rotor to the rotary drive means above, and outside, the material in the hopper and by connecting one end of the stator to a fixed joint positioned below, and outside, the material and the other end to a flexible tube surrounding the discharge outlet of the hopper. The flexible joint permits the orbitable and rotatable motion required of the rotor while the fixed joint and flexible tube permit the orbitable motion required of the stator. And this is done while eliminating the submerged joints and shaft seals of pumps, as shown in the prior art.
Accordingly, prior to this invention, there was a need for a progressing cavity pump for discharging material, such as explosive water gel or other viscous material, from a hopper without requiring the mechanical joints connecting the operating parts of the apparatus to each other be immersed in the material being discharged, while still permitting the unique motion required of the stator and the rotor. This invention, in solving this problem, and problems brought about by mechanical shaft seals, for example, provides such a pump and in doing so gives to the material handling art improvements heretofore not known to such art.